The present invention relates to chart drives for oscillographic recorders and is particularly directed to a micro-stepping motor control circuit.
Driving the chart in an oscillographic recorder requires precision control of the driving motor. The prior art has taught two basic methods of driving the chart in the oscillographic recorder. The first and most prevalent consists of a synchronous A.C. motor, a mechanical transmission with gear ratios selected by soleniods. The second method is to use a D.C. servo system with a D.C. motor is combination with a tachometer.
The synchronous A.C. motor system requires a transmission consisting of precision gears and clutches. This type of system is difficult to assemble and is quite noisy in operation. Also the speed of the chart paper is not adjustable. It depends on the frequency of the A.C. line, and the build up of all the mechanical tolerances in the system. As parts wear, the chart speeds will tend to get farther and farther away from their nominal values. Also with a synchronous A.C. motor system, it is difficult to provide non-standard chart speeds since this would require a design for a new transmission. A separate transmission would be needed for 60Hz and 50Hz line frequencies.
In the D.C. servo system, difficulties arise in low speed operations since the voltages generated by the tachometer are very small. A good deal of calibration is required in this type of system. D.C. motors of sufficient torque to drive a chart in an oscillographic recorder that are small in physical size are quite expensive.